Differential Equations and Linear Algebra (4th Edition)

Published by Pearson
ISBN 10: 0-32196-467-5
ISBN 13: 978-0-32196-467-0

Appendix B - Review of Partial Fractions - Exercises for B - Problems - Page 803: 16

Answer

\[\frac{x(2x+3)}{(x+1)(x^2+2x+2)}=\frac{-1}{(x+1)}+\frac{3x+2}{x^2+2x+2}\]

Work Step by Step

Because $x^2+2x+2$ has no real zero so we can not factor it so In this case the general form of the partial fraction decomposition is \[\frac{x(2x+3)}{(x+1)(x^2+2x+2)}=\frac{A}{(x+1)}+\frac{Bx+C}{x^2+2x+2}\;\;\;...(*)\] \[2x^2+3x=A(x^2+2x+2)+(Bx+C)(x+1)\] \[2x^2+3x=A(x^2+2x+2)+(Bx^2+Bx+Cx+C)\] \[2x^2+3x=(A+B)x^2+(2A+B+C)x+(2A+C)\] Compare like coefficients both side \[A+B=2\;\;\;...(1)\] \[2A+B+C=3\;\;\;...(2)\] \[2A+C=0\Rightarrow C=-2A\;\;\;...(3)\] Using (3) in (2) then (2) becomes \[B=3\] From (1) \[A=-1\] From (3) \[C=2\] From (*) \[\frac{x(2x+3)}{(x+1)(x^2+2x+2)}=\frac{-1}{(x+1)}+\frac{3x+2}{x^2+2x+2}\] Hence, \[\frac{x(2x+3)}{(x+1)(x^2+2x+2)}=\frac{-1}{(x+1)}+\frac{3x+2}{x^2+2x+2}.\]
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